The authentication of objects (e.g., documents, money or pharmaceuticals) has been an important endeavor for thousands of years. It will, similarly to encryption and code breaking, continue to be a significant and constantly evolving problem for the indefinite future. While a great deal of effort has been expended with respect to the development of Information Technology related security issues, the physical encoding of samples to identify, track and validate objects or samples is also critically important. The considerable financial and physical losses that result from counterfeiting and the lack of widespread, accurate and inexpensive authentication technology permeate every aspect of society. Examples include document forgeries, illegal duplication of software and optical media, branded consumer goods, technical intellectual property theft and pharmaceutical tampering.
One method to identify objects is to optically encode them, which is to say that an object combined with an optically active material can be identified by emitting a unique spectral or optical signal or signature upon undergoing suitable excitation. Previously known systems for optically encoding objects or samples have a fundamental problem: they cannot support a very large number of unique codes which means only small numbers of samples can be measured. A unique identifying code is related to a unique optical emission signature. In nearly all cases, the optical code is generated by observing ratios of two or more emitting components in a mixture. However, if the emitters are organic dyes or quantum dots, their short, excited state lifetimes lead to broad emission peaks, each of which can occupy a large swath of the visible spectrum. Therefore, when two or more components are mixed to create a desired ratio that emits a code of interest, it is difficult to deconvolute the broad overlapping peaks. This is starkly reflected in that the most extensive, commercially available code currently consists of only two dyes resolvable at 1% compositional intervals giving a maximum of 100 samples that can be labeled uniquely.
Therefore, there exists a significant need in the art for a method of optically encoding an object or sample such that truly large numbers of codes can be obtained and used to encode very large numbers of objects or samples which can then be uniquely identified.